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Every single cell in a multicellular organism can in principle trace its "ancestry" back to the zygote through a continuous chain of cell divisions. How many divisions have occurred in a typical cell in an adult human body since the zygote was fertilized?

Obviously the answer depends on the organism's age and on the type of cell (as different types of cells divide at different rates). To be concrete, what is the average number of cell generations from the zygote across all the cells in, say, a typical 25-year-old human?

(Or any other age, if that's more convenient to estimate. I'd also be curious about the approximate minimum and maximum number of divisions, and which types of cells they occur in. If it's too difficult to estimate these statistics over the whole organism, I'd be interested to know if there are any specific types of specialized cells for which it's possible to estimate the "generation number".)

To be clear, I'm not asking about the maximum number of times that a cell can divide. I'm asking about the average number of times it has divided at a given point in time.

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    $\begingroup$ As a starting point for further exploration, Fig. 1 of this paper shows an association between different cancer types and the lifetime total divisions for the stem cell subtypes from which those cancers are derived. The authors give their derivations of the replication rates for each subtype in the supplement (PDF download). $\endgroup$
    – acvill
    Dec 19, 2019 at 16:17
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    $\begingroup$ What type of cell? For instance, AFAIK red blood cells don't divide at all, they are produced by other cells in the bone marrow. I would expect the same is true of other kinds of cells, such as sperm cells. $\endgroup$
    – jamesqf
    Jan 27, 2021 at 19:00
  • $\begingroup$ What research have you done on the subject? this is something you could google. $\endgroup$
    – John
    Jun 27, 2021 at 2:13
  • $\begingroup$ E[MAX(X(t))] of the sampling distribution is the not the same as the largest value in the support for X(t)'s distribution function. It is a sensible to similarly wonder about the maximum number of times it has divided at a given time point $t$. $\endgroup$
    – Galen
    Jun 27, 2021 at 18:56

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The supplemental material of the paper that Dirigible references in a comment to my question gives a rough estimate of these values. If I understand their simple model correctly, then we can estimate the average number of times that the stem cells in various types of tissues have divided over an 80-year lifespan from Table S.1 by finding the row corresponding to a cancer of that tissue, and then calculating $\log_2(s) + d$, where $s$ and $d$ are given in the table. (For specialized cells, I guess you'd add 1 more to capture the final cell division that produces the specialized cell?)

I haven't done the math out, but glancing over the table, it looks like the generation number varies widely between tissues, from a low of about 27 for some brain cells to a high of almost 6000 for cells in the colon and rectum.

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    $\begingroup$ Please edit your post to include the actual citation of the paper. It's not clear what paper you are referencing. Thanks $\endgroup$ Jan 27, 2021 at 12:53
  • $\begingroup$ @theforestecologist - The paper is Variation in cancer risk among tissues can be explained by the number of stem cell divisions. The supplementary material is found by clicking on the link near the end of the article. $\endgroup$
    – mmesser314
    Jun 26, 2021 at 22:54
  • $\begingroup$ The supplementary material says epidermal stem cells divide about every $48$ days, typical stem cells divide about every $5$ days, oral mucosa stem cells divide every $14$ to $20$ days, etc. Some cells seldom divide. Carcinoma cells tend to divide much more frequently than average cells. $\endgroup$
    – mmesser314
    Jun 26, 2021 at 23:00

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